Improved asphalt compositions



United States Patent Patented Mar. 20, 1962 ()fice 3,026,280 IMPROVED ASPHALT CGMPGSITIONS David Apotheker, Anchorage, Ky., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Aug. 19, 1959, Ser. No. 834,669 4 Claims. (Cl. 260-285) The present invention is directed to bituminous compositions which may be utilized in road-making. This invention is more particularly related to improving such bituminous compositions by incorporating therein certain copolyrners of chloroprene.

It is known that incorporating small amounts of polychloroprene under certain conditions into asphaltic materials greatly improves certain physical properties which are closely related to the performance of these asphalts as road-making materials. Even though the amount of neoprene used is of the order of only 3% of the asphalt, the increased cost on a percentage basis for a relatively very cheap material such as asphalt is high. This increase in cost is justified by the improvement in the properties of the asphalt, expressed in much longer life for the road surfaces made therefrom. The need, however, for an additive giving the same effects when used in even smaller amounts is obvious.

it has now been discovered that certain copolymers of chloroprene with 2,3dichlorobut-adiene-1,3 have a significantly greater effect than polychloroprene itself on asphalt. It has also been discovered that these copolymers of chloroprene may be utilized in significantly smaller amounts to produce the same elfects as achieved with the comparative prior art polymers.

It is an object of this invention to provide novel bituminous compositions having import-ant utility in roadmaking. It is a further object of this invention to provide such novel bituminous compositions by incorporating therein certain copolymers of chloroprene as hereinafter described. These and other objects will become apparent in the following description and claims.

More specifically, the present invention is directed to a composition comprising a bituminous material having incorporated therein about 0.01 to 5.0% of a plastic copolymer of chloroprene and 2,3-dichlorobutadiene-L3 made from a monomer mixture containing 20 to 80% of the latter and 0.1 to 0.7% an aliphatic mercaptan. Preferably the amount of copolymer incorporated is between 0.75 and 3%, the proportion of dichlorobutadiene between 30 and 60% and the proportion of mercaptan 0.2 to 0.4%.

The copolymer utilized according to this invention is preferably made in aqueous alkaline emulsion in which the dispersing agent is a salt of a long-chain fatty acid or rosin acid. The polymerization is usually stopped when 50 to 95% and preferably about 65-75% of the monomer mixture has been polymerized. The unchanged monomers are then removed by distillation, a convenient method which avoids foaming and coagulation of the latex involving steam distillation under conditions of turbannular flow, as taught in US. 2,467,769. The aliphatic mercaptans prefer-ably contain 6 to 18 carbon atoms and preferably are saturated, primary and unbranched. Examples of this preferred class are n-hexyl, octyl, dodecyl, and stearyl mercaptans. Examples of the less preferred secondary and tertiary mercaptans are the tertiary dodecyl, tertiary tetradecyl, and secondary tridecyl mercaptans.

The conventional catalysts used for the polymerization of dienes and particularly of chloroprene may be used here. Examples of these are ferricyanides and persulfates. Similarly, the usual short-stops, such as de cribed in US. 2,576,009 may be used. These also serve as stabilizers for the isolated polymer. rubber antioxidants may also be added.

The copolymers are preferably incorporated in the asphalt by direct mixing of the latex or by incorporating the soiid copolymer in finely divided form, such as is obtained by spray drying or by grinding at low temperature. In any case, the asphalt must be in fluid form, either fused or in solution. A convenient method for incorporating latex into asphalt on a large scale involves injecting a stream of latex into molten asphalt at 140 to 180 C. and then passing the mixture through a tube under condition of turbannular flow, whereby the elastomer is uniformly incorporated in the asphalt and the water of the latex is removed as steam Without objectionable foaming.

Representative examples illustrating the present invention follow.

A copolyrner typical of those used in the present invention is made by emulsifying 60 parts by weight of chloroprene and 40 of 2,3-dichlorobutadiene-l,3 containing 035 part of primary normal dodecyl mercaptan and 3 parts of disproportionated resin in 109 parts of water containing 0.55 part of sodium hydroxide, and 0.3 part of sodium sulfite, the rosin being neutralized by the sodium hydroxide to form the emulsifying agent. The catalyst, a 10% aqueous solution of potassium ferricyanide, is added as needed to maintain the polymerization at 30 C. The polymerization is stopped by adding a dispersion of phenothiazine (thiodiphenylamine) and p-tertiary butyl catechol when 70% of the total monomers have been polymerized. The unchanged portion is then removed by steam distillation by passage with steam at reduced pressure through a tube under conditions of turbannular flow, referred to above.

Other copolymers within the scope of the present invention are made by obvious variations of the heretofore described procedure.

EXAMPLE 1 The described copolymer latex is incorporated into an asphalt of -100 penetration grade so as to give 1.5 parts of copolymer per parts of asphalt. To do this, the asphalt is heated to C. and the latex is added slowly with agitation. The water boils off, excessive foaming being avoided by slow addition of the latex. A good dispersion of the copolymer in the asphalt results.

The following tests were applied:

Tests Low temperature ductility: (ASTM-D-l13-44). This is measured by mechanically pulling a molded briquet of asphalt at 4 C. at a rate of pull of 5 cm. per min. until it breaks and measuring the length of the specimen in centimeters at the breaking point.

Benson pull-test: (Benson, Jewell R.-New Concepts for Rubberized Asphalts, Roads and Streets, April, 1955 A 'Ms-inch diameter steel hemisphere is embedded in a hot asphalt blend so that the flat surface is flush with the asphalt surface. The asphalt (35-40 ml.) is contained in a 3-ounce seamless ointment can. After conditioning the sample at 25 C. for 24 hours, the head is pulled from the sample at a constant rate of 20 inches per minute using the Instron or Scott tester. The area under the long-pull portion of the curve, an area bounded by a line being drawn from the initial peak load point to the zero force axis, corresponding in inch/pounds done upon the sample. is the tenacity of the material. The results are given in the accompanying tables, along with those obtained using for comparison unmodified asphalt and asphalt modified by incorporating ordinary polychloroprene.

The copolymer used in Example 1 is incorporated in Conventional the same way into asphalt in other proportions tougive the compositions of Table I. The copolymer used in Tables II'and HI are made like that usedin Example 1,

With the indicated Variations in the amounts of mercaptan, and of 2,3-dichlorobutadiene, and in the percentages of monomers converted.

TABLE renrnno'r oavirtyme Tnn .tnowror oo'PoL- YMER ONTHE rnornn'rrns on TnnAsPnALT *Made by the same general procedure as the copolymer userlin the 7 other compositions of the table. 7 It can be seen in this table that the copolymer ,produces an observable effect at a concentration as low as 0.01% and that the eiiect of 0.75% is somewhat greater than the effect of 1.5% of polychloroprene, Still further increasein the amountof the copolymer furtherincreases theductility and tenacity but not to as great an extent. Above 5%, the copolymer tends to gel.

TABLE II.-EFF,EGT OF VARYING THE. AMOUNT DEE-115R- CAPTAN USED IN MAKING THE OOIOLYMEROF EX- AMPLE 1 (1.5 PARTS OF COPOLYlVIER'USED IN 100 PARTS OF ASPHALT THROUGHOUT) V .Parts of Dodecyl Mclcaptans Per 100 Parts of Monomer Dnctility:

last line). TABLE IIL-EFFECT or VARYING Tar. mover OF DIOHLOROBUTADIENE AND THE PERCENT CONVER I SION OF THE MIONOINIERS Y Percent Dichlorobutadiene in Percent Con- J p the Monomer Mixture version 01' the Y Ductility Tenacity Monomers" '60 v v 47 70 137 1 80 27 00 133 V 50 146 70 54 143 90 -58 V 155 150 60 27 60 140 47 90 117 0 7O 25 90 The above results-were obtained for 1.5 of the poly- 7 inei n1 asphalt. 'Eachipolynie'riwasgmade wiiiifoiss part of dodecyl mercaptan.

"Table III indicatedthat, in general, the-best results are obtained by using about 40% of the 2,3-dichlorobutadiene-l,3 in the monomer mixture and by polymerizing to about 70% conversion. Again, however, all the copolymers tested gave greateneffects .than the same quantity of polychloropre'ne." v H Although the ,above examplesfillustrate the use of only dod ecyl mercaptan as the modifying; or chain' transfer agenL the use of other mercaptans within the limits of the invention could similarly-befully. illustrated, if space allowed. For example, n-hexyl mercaptan used in place of dodecyl mercaptan in 'makin'g'thecopolymer used in Example 1 gives identical res'ults,while tertiary tetradecyl mercaptan, an example a of the less; preferredclass of branched mercaptans,-'gives a tenacity oil-01, which is still much greater than the etfectiof the "same quantity of polychloroprene. It is often advantageousto use mixtures of mercaptans and'to add part ofthe mercaptan during the. course 'of the polymerization.- Thus the preparation of the copolymer used in Example 1 may: be modified by using only 0.2 part of'dodecyl mercaptan at the start and adding 0.15 part oftertiary tetradecyl mercaptan When tlie conversion reaches 50%. 'When the polymerization is carried to 1.5% of the product still gives a tenacity of 143 in asphalt.

As many apparently widely different embodiments of this invention may be made withoutdeparting from the spirit and scope thereof, it isto be understood-thatthis invention is not limited to the specificembodiments thereof except as defined in the appended-claims. p

The embodiments of'the invention in which an exclusive property or 'privilege is claimed are defined as follows: i i v -l. A composition comprising anasphalt'having incorporated therein from about 0.0-1 to about 5.0% based on the weight of said asphalt of a plastic copolymer of chloroprene and 2,3-dichlorobutadiene-lg3,said copolymer being made from a monomeric mixture of chloroprene and 2,3-dichlorobutadiene-1,3, said monomeric mixture containing 20-80% by weight of 2,3-dichlorobutadiene-l,3 and from 0.1 to 0.7% of an aliphatic mercaptan.

2. A composition comprising an asphalt having incorporated therein from about 0.75 to' about 3% based on Hthe weight of said asphalt of a plastic copolymer of 'chloroprene and 2,3-dichlorobutadiene-l,3, said copolymer being made from a monomeric mixture of chloroprene'and 2,3-dichlorobutadiene-1,3, said monomeric-mixture containing 30-60% by weight of 2,3-dichlorobutadiene-l,3 and from 0.2 to' 0.4% of an aliphatic mercaptan;

References Cited in the file of this'patent UNITED STATES PATENTS 2,493,793 Abernathy et a1. ,Jari. 10 1950 2,868,749 7 Hugg Jan. 13, 19,59 

1. A COMPOSITION COMPRISING AN ASPHALT HAVING INCORPORATED THEREIN FROM ABOUT 0.01 OT ABOUT 5.0% BASED ON THE WEIGHT OF SAID ASPHALT OF A PLASTIC COPOLYMER OF CHLOROPRENE AND 2,3-DICHLOROBUTADIENE-1,3 SAID COPOLYMER BEING MADE FROM A MONOMERIC MIXTURE OF CHLOROPRENE AND 2,3-DICHLOROBUTADIENE-1,3, SAID MONOMERIC MIXTURE CONTAINING 20-80% BY WEIGHT OF 2,3-DICHLOROBUTADINE-1,3, AND FROM 0.1 TO 0.7% OF AN ALIPHATIC MERCAPTAN. 